Selective sorption of Ce³⁺ over La³⁺ ions on biogenic manganese oxides

Unique properties of biogenic Mn oxides were applied to a fundamental study of separation and recovery of rare earth elements. Selective sorption of Ce³⁺ over La³⁺ ions was achieved at neutral pH values using biogenic Mn oxides produced by Paraconiothyrium sp. WL-2 strain. The selective coefficient for Ce3+ (α_Ce) was much greater with biogenic and synthetic Mn oxides than those for La³⁺ (α_La). Ce³⁺ ions were oxidized to CeO₂ by Mn(III, IV) in Mn oxides under anaerobic conditions resulting in the release of Mn²⁺ ions, while La³⁺ ions were sorbed without a redox reaction. With an increase in coexisting La³⁺ ions, sorption of Ce³⁺ on both Mn oxides was significantly suppressed, especially with synthetic Mn oxides. The edges of the structure are competitive sites because of fewer numbers of vacant sites in synthetic Mn oxide layers. The preferential sorption on the edge sites of Mn oxides is in the order of La³⁺ > Ce³⁺. These phenomena can be expanded to separation and recovery of other rare earth elements from natural and anthropogenic sources.